Lockout circuit



April 2, 1957 w. METZGER LOCKOUT CIRCUIT Filed Aug. 3, 1953 7'0 SCREEN INVENTOR E W METZGER mww ATTOR EV.

This invention relates to lockout and selection, circuits and more particularly to circuits for reliablypreventingsimultaneous actuatiorrof morethan .one worlccii cuit of a group from which. it is desired to make av single selection.

In many kinds of control mechanism a..plur ality of:

work circuits is provided and control ,circuits -usually including vacuum tubes are employed selectively to ace tuate the woric circuits in response to. externally supplied control signals. In one .commoncircuit,of.;thi s general nature, eachof the work circuits is actuated by a relay,

the winding ofb which is included, inthe anode circuit of a gaseous discharge or thyratron tube and isetfective when discharge occurs in the tubeto operate connected A control signal: from-an external; source ;.is

circuits. applied selectively tethe control ,elementsof the appropriate one of the several discharge, tubes whenever, it is; desired to cause operation pithe Workeircuitassociated therewith. Often, such control signals are transmitted over considerabledistances bymeans ofj'a common, trans;

mission facility and are distinguished from each other on In-.either a frequency basis or bytitne of occurrence, event, the presence otjnois'ejn thetransm-ission.facility.or. malfunctioning ofthe selective' transmitting device .-n1ay sometimes result inthe simultaneous application ,of more than one signal capable of actuatinga discharge tubetand itswork circuit; Under. these oircumstahc es, work circuits other than thatdesiredtobeiactuatedwill respond. i d fiiw f..t v= s;. p t c lar y und irab awhe the several worlg circuitsconstitute means for'subs tit-uting,

alternative transmission facilities in, a signalingsysterrr or. the interconnection of a desiredcne of a number of alter native controlled circuits in vari'ous industrialprocesses;

Dithculties of the kind referred ro aboveare commonly, obviated by means of so-called loclgout circuits often r involving the interconnection ofilarge numbers ofrelays, or discharge tubes in ,such a way that, operation: of one relay or tube efiectively prevents operation of'any of. the, 4

others. Such relaycireuits maynot, however, besutir ciently rapid in operationforsujch applications as those involved in the automaticswitchingcf tran mi ioniacilities as disclosed,'for example, in the copen rigapplication of. I. B. Maggie, SerialNo 3 09,51 47, filed September 13, th rJknQ n l ckoutc rm ts h ,may .v increased"operating speeds suffer from la c l of reliable p tion nde l circu ta ces. lath pp ic ticnq selection. circuits, of thejtype centemplated ,to commun Cation ci i es c 'cv n one fail tcil ft qs eb icnd v se camb t e a d. esp t r a r lr de. acation he;

operating conditions,

i is e object f; epres n i nv nt on, er to e,to provide reliable high speed lockout andselect ion circuits for; correcting false operationinyolvingjthejunwanted c p ticn. f. rcthaaj one n rp l cl' Opera he broughtabout y h m ltansqus" nl sati i fi nt sii signalsor by spurious'signals reaching thecontrol elements. The lockoutor-selection-circuit according to the inven;

"nited States Patent ice tion comprises a plurality of discharge tubes, each con:

trolling an individual workicircuit in response to an individual contrclsignal.- The anode circuitsoftheseveral,

discharge tubes each including the actuatingrelement of. the associated 'Work' circuit are connected in parallel, through a common impedance to a source of operatingpotential. A second impedance shared in common by the cathodes of the several discharge tubes completesthe operating anode-cathode circuits for the tubestand addi'e; ticnal impedances are connected across the source of potential to form atom-arm bridge circuit, onearm ofj which comprises the first-mentioned commoni'rnpedance and the. parallel-connected anode circuitsandassociated discharge tubes. are so proportioned'thatthe bridge isin eliect balanced only when fewer than two of thedischargetubes vare conducting. A detector is connected across the diagonal of the bridge not including the source of potential and is responsive to a particular unbalanced condition on the,

bridge effectively to remove the operating potentials from the discharge tubes.

The above and other features of the invention will be describedin the followingspeciiication takenin connec:

tion withthe drawings the singlefigure of which is a schematic circuit diagramcf a selection circuit according tones, one for eachdesired operation, transmitted in commen over a line andiseparatedby frequency discrimination for applicat-ion to-the control-circuit of the, invention. ln-the drawingthree of a plurality of controlled relays 10;; 12 and l t/are illustrated; ltjwill'be understood that each of these relays serves upon operationto establish desired" circuits throughactuation of its associated armature. These circuits are notillustrated and may take any form desired-depending upon-the nature of the operation to be.

performed;

Each of relaysfltl, 12 andl i'constitutes a portion of* the anode load of a discharge tube, the three relay windings being associated 'withdischarge tubes 16; 18 and 20 respectively, by wayof load resistors 22, 24 and 26. The several dischargetubes are-shown as comprising gaseous,

discharge-tubes of the type commonly referred to asthyratrons, but it isto be understood that depending upon the application to be made of the selectioncircuit, vacuum tubes may also be employed. Further, it is to be understood that although only three work circuits ltl, 12- and;

14" and associated discharge tubes are shown in the drawing, additional circuits maybe added as desired and-connected between lead 28 and asecond lead 3%), the anode circuits of all= control tubes being connected in common to the first lead, andthecathode circuits ofthe tubes being connected in common to the second lead. Theindividual control signals for tubes 16, 18 andZiE-rnay be applied, to the control grids thereof in the usual manner through terminals 32, 34 and'fifi respectively. The screen gridsof-the-sever-al tubes are provided with operating potentials and their control grids with suitable biases in-the usual 'way, all details of these circuits notbeing'shown, however, in the drawings It will be recognized that the several discharge; tube circuits eachincluding; the operating winding of the associatcd relay as-an anode lead, are connectedin parallel betWeen-le'ads 28 andStl. These parallel connected circuits are connectedin series throughal resistor 38 to; the,

aten p .57

Theseveralimpedances of the bridge positive terminal of a battery 40, the negative terminal of which is grounded. Similarly, lead 30 provides means for connecting these parallel circuits to ground through the normally closed contact 42 of a relay 44, a series resistor 46 and battery 47, the positive terminal of which is grounded. Batteries 40 and 47 thus supply operating potential to any of the discharge tubes connected between leads 28 and 30, so that upon application of a suitable control voltage discharge current can be caused to fiow in any one of the discharge tubes.

As has been suggested heretofore, it may be especially desirable in certain applications of control circuits of the general type here involved to insure that not more than one work circuit is actuated at a time, regardless of whether more than one control signal is present, or regardless of the amount of noise present in the control circuits. For this purpose, and in accordance with the invention, additional impedances shown in the drawing as resistors 48 and 50 are connected in series between the positive terminal of battery 40 and the negative terminal of battery 47. It will be recognized that these additional impedances together with resistor 46 and the impedance comprising the paralleled anode circuits and discharge tubes 16, 18 and 20 in series with resistor 38 constitute a four-arm bridge circuit across one diagonal of which the batteries 40 and 47 are serially connected. The other diagonal of this bridge extends from the junction of resistor 46 and the armature of relay 44 to the junction of resistors 48 and 50.

As mentioned above the impcdances constituting the arms of the above described bridge circuit are so proportioned that the bridge is in a condition herein referred to as effectively balanced only when fewer than two of the discharge tubes is conducting. Thus, when respectively (1) one or (2) none of the tubes is conducting the parallel impedance comprising their several anode-cathode circuits is sufficient (l) to balance the bridge within a required degree of precision or (2) to unbalance it in an ineffectual direction. In both of these conditions the bridge will be herein referred to as effectively balanced. If, however, two or more of the discharge tubes become conductive, the impedance of the arm of the bridge in which they are located in sufiiciently reduced to unbalance the bridge in an effectual direction. A detector of suitable sensitivity to discriminate between these conditions may then be connected across the second diagonal of the bridge and may be made responsive to the lastmentioned unbalance of the bridge to effectively remove the operating potential from the several discharge tubes.

In accordance with further features of the invention, the detector is made efifective, first to reduce the current drawn through the work circuit by any operated discharge tube to such an extent that the work circuit is released, and, second, completely to remove operating poten tials from the discharge tubes to cause their deionization preparation to resetting the circuit for further operation. The first action of the detector, namely that of reducing the potential applied to the discharge tubes to such an extent that the work circuits are released takes place substantially instantaneously and permits reliable operation of the device at high speeds. Additional apparatus to be described hereinafter is also provided for reapplying operating potentials to the discharge tubes after a predetermined interval of time thereby resetting them to permit the selection of work circuits in the event that at a later time only one control signal is present at the input terminals.

Conveniently, and as shown in the drawing the detector may comprise an additional discharge tube 52, having its cathode connected to the junction of resistors 48 and 50 and its anode connected to the positive terminal of battery 40 by way of resistor 38 which it therefore shares with the anode circuits of control tubes 16, 18 and 20. The potential appearing across the second diagonal of the bridge is applied through resistor 56 and current limiting resistors 54 and 58 to the control and screen grids of the tube, resistor 56 together with capacitor 57 serving as a filter to prevent transient voltage surges from reaching the detector tube. When the bridge is balanced this potential will have a value near to zero with the effect that both grids of the tube 52 will be at substantially the same potential as its cathode. Thus they will shield the cathode from the anodes potential and the tube wiil not fire. Similarly it will not fire when the bridge is unbalanced to any extent in the above-mentioned ineffectual" direction because the same two grids will actually be negative with respect to the cathode. Thus it is seen that the bridge may be proportioned for three possible conditions of balance: (1) effective balance," i. e., either actual balance or, what may be deemed equivaient thereof, a relatively small amount of unbalance in an ineffectual direction when just one of the tubes i6, i8, and 20 is conducting (or, if desired, just some other predetermined number greater than one); (2) a relatively large amount of unbalance in the ineffectual direction when less than that number is conducting; and (3) effective unbalance, i. e., an operative amount of unbalance in an opposite and effectual direction when more than that number is conducting.

Provision is made for the fact that the return path over resistor 50 and battery 47 may be inadequate to carry the intended cathode current of the tube 52 if high value bridge impedances are used for the conservation of power. Accordingly, a second return to ground is provided by way of a varistor or rectifier 60. When the bridge is balanced the cathode of tube 52 is negative with respect to ground as the voltage drop across resistor 59 in the voltage divider 48, 50 is less than the voltage of battery 47. To this end the ratio between the values of the resistors 48 and 50 should be related to the ratio of the voltages provided by the batteries 40 and 47. As a result, varistor 60 is normally non-conducting and there fore does not interfere with the intended condition of balance of the bridge since its impedance to ground from the horizontal diagonal of the bridge and across its right lower arm will have a high value until such time as an effective unbalance produced by the firing of more than one of the switching tubes causes the establishment of discharge current flow in the detector tube.

In the operation of the circuit as thus far described any unbalance at the bridge caused by the simultaneous establishment of discharge current through more than one of relays 10, 12 or 14 by virtue of, say, the simultaneous presence of two or more control signals unbalances the bridge to a suificient extent to drive both grids of the discharge tube 52 positive and thus cause it to break down. Discharge current through this tube flows through resistor 38 in such an amount as to cause a large drop of potential 'thereacross. The reduced potential at the left hand terminal of resistor 38 and therefore upon lead 28 is so low that none of the operated control tubes can draw sutficient current through the associated relay windings to maintain the work circuits actuated. The work circuits are therefore released very rapidly whenever the bridge becomes unbalanced.

If, as shown in the drawing, the control tubes 16, 18 and 20 are gaseous discharge or thyratron tubes such reduction in the anode potential, while suflicient to disable the work circuits will not serve to extinguish the tubes. For this purpose, the anode of detector tube 52 is also connected to the positive terminal of battery 40 by way of the primary winding of a differential polar relay 62 and a series resistor 64. The circuit constants are so arranged that relay 62 operates whenever discharge current fiows in detector tube 52. Operation of relay 62 serves to complete an operating circuit for relay 44 which may be traced from the negative terminal of battery 68, the operated contact of relay 62, the winding of relay 44, resistor 38 and battery 40 to ground. Operation of relay 44 serves to open normally closed contact 42, thus interrupting the cathode circuits of the control tubes 16, 18 and 20 which are thereupon extinguished. At the same time it applies the negative pole of a battery 68 through the winding of the relay 44 to the common circuit which normally energizes all of the discharge tubes 16, 18, 20 and 52 thereby extinguishing the tube 52 which will not have been quenched along with the other tubes by operation of the relay 44. This will take place even though the positive terminal of the battery 40 remains connected to this common circuit since during this operational step substantially all of the potential of the battery 49 will be lost as a voltage drop across the resistor 38.

Operation of relay 62 also opens the circuit including battery 68, resistor 70 and battery '72. The connection to battery 68 having been removed, battery 72 begins to charge a capacitor 74 positively through the series circuit including resistor 70 and completed by way of ground. A discharge tube 76 is connected in series with a secondary winding of relay 62 and across capacitor 74. When the potential across capacitor 74 reaches such a value as to ionize the discharge tube 76, it breaks down and current flows therethrough. The time at which this occurs following initial operation of relay 62 upon unbalance of the bridge is determined by the RC circuit comprising resistor '70 and the capacitor 74.

The flow of current in discharge tube 76 passes through the secondary winding of relay 62 in such a direction as to return this relay to the original position. Release of relay 62 in turn permits release of relay 44 re-estab-lishing the cathode circuits of the control tubes and preparing them for operation in respect to any control signals then present at input terminals 32, 34 and 36. At the same time, the re-establishment of the circuit over the unoperated contact of relay 62 extinguishes discharge tube 76 since the same potential (from battery 68) is applied to both of its terminals. This completes the restoration of the control circuit to its original condition. If, at this time, only one control signal is present on the input to the controlling tube, the associated work circuit may be actuated. If, on the other hand, more than one control signal is still present at the input terminals, the cycle of operations just described will be repeated until such time as only one control voltage is present.

What is claimed is:

1. In a lockout and selector circuit a plurality of discharge tubes each controlling an individual work circuit and having at least anode, cathode and control grid elements, individual means for abruptly switching over each of the tubes from a substantially non-conducting to a conducting condition, a four-arm bridge one of the arms of which includes the said discharge tubes in parallel, and the other arms of which are proportioned for a predetermined condition of effective balance of the bridge only when fewer than a predetermined number of said tubes are conductive, a source of potential connected across one diagonal of said bridge to supply anode current for said tubes and means responsive to a predetermined eifective unbalance of said bridge to interrupt conduction in all of said tubes.

2. In a lockout and selector circuit a plurality of discharge tubes each controlling an individual work circuit and having at least anode, cathode and control grid elements, individual means for abruptly switching over each of the tubes from a substantially non-conductive to a conductive condition, a four-arm bridge one of the arms of which includes said tubes in parallel, and the other arms of which are proportioned for a predetermined condition of effective balance of the bridge only when fewer than two of said tubes are conductive, a source of potential connected across one diagonal of said bridge to supply anode current for said tubes, a detector connected across the other diagonal of said bridge and means responsive to said detector upon a predetermined effective unbalance of said bridge for interrupting conduction in .all of said tubes.

3. In a lockout and selector circuit'a plurality of discharge tubes each controlling an individual work circuit and having at least anode, cathode and control grid elements, a four-arm bridge one of the arms of which includes said tubes in parallel, and the other arms of which are proportioned for balance of the bridge only when fewer than at least two of said tubes are conductive, a source of potential connected across one diagonal of said bridge to supply anode current for said tubes, a detector connected across the other diagonal of said bridge, means responsive to said detector upon a predetermined unbalance of the bridge for effectively removing the operating potential from said tubes, and a timer circuit started by said detector upon said unbalance of the bridge and effective after a predetermined interval to :disable said potential removing means to permit further operation of said control tubes.

4. in a lockout and selector circuit a plurality of gaseous discharge tubes each drawing current through and controlling the operation of an individual work circuit when fired in response to individual control signals, a source of operating potential for said tubes, an impedance connected in a common circuit between said source of potential and the anodes of all of said tubes, said impedance and the parallel impedance of said tubes comprising one arm of a four-arm bridge, the remaining arms comprising first, second and third impedances, said first impedance being connected as a cathode impedance in common for all of said tubes, means for connecting said source of potential across one diagonal of said bridge to supply operating potentials to said tubes, and a detector connected across the other diagonal of said bridge and responsive to an unbalance of the bridge upon simultaneous conduction of at least a predetermined plurality of said tubes to effectively remove the operating potentials therefrom.

5. In a lockout and selector circuit a plurality of discharge tubes each controlling an individual work circuit and having at least anode, cathode and control grid ele- 1 ments, a four-arm bridge one of the arms of which includes said tubes in parallel, and the other arms of which are proportioned for a predetermined condition of effective balance of the bridge only when fewer than at least two of said tubes are conductive, a source of potential connected across one diagonal of said bridge to supply anode current for said tubes and means responsive to a predetermined effective unbalance of said bridge to reduce the current in any of said tubes which are conducting disabling the work circuits controlled thereby, means also responsive to such unbalance thereafter to remove the operating potentials from said tubes to extinguish the flow of current therein, and means for reestablishing said operating potentials for said tubes after a predetermined time interval.

6. In a lockout and selector circuit, a plurality of discharge tubes each responsive to an individual signal to control an individual work circuit, means for connecting said tubes in parallel, an impedance shared in common by the cathode circuits of said tubes, additional impedances connected to complete a bridge circuit adjacent arms of which include said parallel-connected tubes and said impedance respectively, the impedances of said bridge being proportioned for a predetermined condition of eflective balance only when fewer than at least two of said control tubes are conductive, a source of potential connected across one diagonal of said bridge to supply operating potentials for said tubes, a detector circuit con nected across the other diagonal of the bridge and means responsive to said detector upon a predetermined eifective unbalance of said bridge efiectively to prevent operation of any of said work circuits.

7. In a lockout and selector circuit a plurality of control tubes each having at least anode, cathode and control grid elements and responsive to an individual signal to control an individual work circuit, means for connecting said tubes in parallel, a source of operating potential for said tubes, 8. first impedance connecting the paralleled anode circuits of said tubes to one terminal of said source of potential, 21 second impedance connecting the paralleled cathodes of said tubes to the other terminal of said source of potential, additional impcdances connected to complete a bridge circuit having said source of potential across one diagonal thereof, a detector tube having at least anode, cathode and control grid elements, means for connecting the grid and cathode respectively of said detector tube across the other diagonal of said bridge, and means connecting the anode-cathode circuit of said detector tube across said source of potential by way of said first inipedance said detector being responsive to a predetermined unbalance of the bridge to draw current through said first impedance to reduce the operating potentials of said control tubes.

8. In a lockout and selector circuit a plurality of con trol tubes each having at least anode, cathode and control grid elements and responsive to an individual signal to control an individual Work circuit, means for connecting said tubes in parallel, a source of operating potential for said tubes, at first impedance connecting the paralleled anode circuits of said tubes to one terminal of said source of potential, a second impedance connecting the paralleled cathodes of said tubes to the other terminal of said source of potential, additional impedances connected to complete a bridge circuit havin said source of potential across one diagonal thereof, a detector tube having at least anode, cathode and control grid elements, means for connecting the grid and cathode respectively of said detector tube across the other diagonal of said bridge, and means responsive to current flow in said detector due to a continued predetermined unbalance of said bridge to open the cathode circuits of said control tubes.

9. in a lookout and selector circuit a plurality of control tubes each having at least anode, cathode and control grid elements and responsive to an individual signal to control an individual work circuit, means for connecting said tubes in parallel, a source of operating potential for said tubes, at first impedance connecting the paralleled anode circuits of said tubes to one terminal of said source of potential, a second impedance connecting the paralleled cathodes of said tubes to the other terminal of said source of potential, additional impedances connected to complete a bridge circuit having said source of potential across one diagonal thereof, a detector tube having at least anode, cathode and control grid elements, means for connecting the grid and cathode respectively of said detector tube across the other diagonal of said bridge, and means responsive to current flow in said detector due to a continued predetermined unbalance of said bridge to open the cathode circuits of said control tubes, said means comprising a relay responsive to current How in said detector and operative also effectively to remove the operating potential from the anode of said detector tube.

References Cited in the file of this patent UNITED STATES PATENTS 

